The long-term goal of this proposal is to elucidate the role of plasrninogen in neurite outgrowth. An emerging area of research has provided evidence strongly supporting a role for molecules of the plasminogen system in neuronal function. This proposal is based on data demonstrating a novel function for plasmin(ogen): augmentation of neurotrophin-stimulated neurite outgrowth independently of proteolysis. Moreover, plasminogen synthesis and promoter activity are up-regulated by nerve growth factor (NGF). These results suggest a positive feedback mechanism by which neurotrophins increase plasminogen expression to further augment neurotrophin-dependent neurite regeneration. The central hypothesis that will be addressed in this proposal is that plasminogen augments neurotrophin-dependent neurite outgrowth and that treatment of ceils with neurotrophins up-regulates plasminogen gene expression. To address this hypothesis we will I) identify the mechanisms by which plasminogen enhances neurite outgrowth. We will a) test the hypothesis that kringle domains within the plasminogen molecule are required for augmentation of neurite outgrowth using mutant plasminogens and isolated kringles; b) test the hypothesis that the effect of plasminogen on neurite outgrowth is due to an interaction of plasminogen with an integrin, using specific inhibitors; c) test the hypothesis that the interaction of plasrninogen with neuronal cells stimulates an intracellular signaling pathway by examining cells for the presence of phosphorylated signaling intermediates. II) We will test the working hypothesis that cis acting elements are responsible for the increase in plasminogen expression in response to NGF. We will a) identify regions containing the responsible cis-acting regulatory elements; b) identify responsible transcription factors; c) test the hypothesis that endogenous neuronal plasminogen can enhance neurite outgrowth and d) test the validity of our working hypothesis in vivo. We expect that accomplishment of our specific aims will provide fundamental insights that may apply to both physiological processes (e.g.neuronal plasticity) and pathological processes (e.g. spinal cord injury) requiring neurite outgrowth. Our results should also provide new information that will lead to increased understanding of disease processes that may be modulated by increases in levels of neuronal plasminogen, leading to increased proteolytic activity in the CNS (e.g. stroke and Alzheimer's disease) [unreadable] [unreadable]